Integrated circuits are the cornerstone of the information age and the foundation of today's information technology industries. The integrated circuit, a.k.a. “IC,” “chip,” or “microchip,” is a set of interconnected electronic components, such as transistors, capacitors, and resistors, which are etched or imprinted onto a semiconducting material, such as silicon or germanium. Integrated circuits take on various forms including, as some non-limiting examples, microprocessors, amplifiers, Flash memories, application specific integrated circuits (ASICs), static random access memories (SRAMs), digital signal processors (DSPs), dynamic random access memories (DRAMs), erasable programmable read only memories (EPROMs), and programmable logic. Integrated circuits are used in innumerable products, including computers (e.g., personal, laptop, and tablet computers), smartphones, flat-screen televisions, medical instruments, telecommunication and networking equipment, airplanes, watercraft, and automobiles.
Advances in integrated circuit technology and microchip manufacturing have led to a steady decrease in chip size and an increase in circuit density and circuit performance. The scale of semiconductor integration has advanced to the point where a single semiconductor chip can hold tens of millions to over a billion devices in a space smaller than a U.S. penny. Moreover, the width of each conducting line in a modern microchip can be made as small as a fraction of a nanometer. The operating speed and overall performance of a semiconductor chip (e.g., clock speed and signal net switching speeds) has concomitantly increased with the level of integration. To keep pace with increases in on-chip circuit switching frequency and circuit density, semiconductor packages currently offer higher pin counts, greater power dissipation, more protection, and higher speeds than packages of just a few years ago.
The advances in integrated circuits have led to related advances within other fields. One such field is sensors. Advances in integrated circuits have allowed sensors to become smaller and more efficient, while simultaneously becoming more capable of performing complex operations. Other advances in the field of sensors and circuitry in general have led to wearable circuitry, a.k.a. “wearable devices” or “wearable systems.” Within the medical field, as an example, wearable devices have given rise to new methods of acquiring, analyzing, and diagnosing medical issues with patients, by having the patient wear a sensor that monitors specific characteristics.
One important characteristic of a patient and, indeed, any user in general, is the core body temperature. Deviations from a normal core body temperature present a threat to a patient's health and can indicate potential illnesses. Some current medical procedures also rely on manipulating the core body temperature, such as therapeutic hypothermia, to improve the outcome of, or prevent injury from, certain medical conditions or events. In addition to medical aspects, certain activities that may elevate or lower the core body temperature could benefit from having the ability for real-time, dynamic measurement of the core body temperature. For example, certain professions, such as the military, first responders (e.g., policemen, firemen, and emergency medical technicians), etc., may face conditions that elevate or lower the core body temperature to unsafe conditions. These professions could benefit from being able to dynamically measure the core body temperature to detect unsafe temperature levels within the body.
Certain non-invasive methods have been developed based on wearable devices that measure, among other parameters, the skin temperature at a location of a user to determine the core body temperature. One such technique relies on correlations between the detected heat flux and skin temperature at specific locations of a user to determine the core body temperature. Another technique—specifically referred to as the zero heat flux (ZHF) technique—relies on a wearable device locally insulating a user's skin at a specific location until the temperature of the skin reaches the core body temperature, creating a region of zero heat flow from the body core to the skin.
Although these techniques exist for being able to detect the core body temperature using a wearable device, these techniques suffer from various issues. For example, with respect to the first technique, there currently exists no reliable way for a wearable device to account for the evaporative heat loss from a user sweating during the detection of the heat flux. With respect to the second technique, there currently exists no reliable way to measure the core body temperature in environments where the ambient environmental temperature is greater than the core body temperature.
Accordingly, needs exist for devices and methods for determining the core body temperature using wearable devices that can account for evaporative heat loss in determining the heat flux at a location on a user or that can measure the core body temperature of a subject in environmental conditions that are hotter than the typical core body temperature.